The present disclosure is related to non-volatile memory devices comprising a reversible resistivity-switching layer used for storing data. The resistivity of this layer can be varied between at least two stable resistivity states such that at least one bit can be stored therein. In particular this resistivity-switching layer is a metal oxide or a metal nitride.
Today the Flash non-volatile memory technology, whereby charge is stored in a conductive or non-conductive charge storage layer incorporated in a MOSFET structure, dominates the market of non-volatile memories. It is expected that this type of non-volatile memory technology will face severe scaling problems beyond the 45 nm technology node due to fundamental physical limitations associated with this data storage mechanism as put forward in the International Technology Roadmap for Semiconductors (ITRS), “2005 edition, Process integration, Devices and Structures”.
Other non-volatile memory technologies are emerging that have the potential of allowing further downscaling of the memory cell dimensions. Among the most promising technologies are resistive-switching memories also known as Resistive Random Access Memory (RRAM). Such a RRAM memory cell comprises a memory element and a selection element. The resistivity of the non-volatile memory element can be reversibly varied between at least two stable resistivity states employing a voltage- or current-induced resistivity change of a material. Examples of such reversible resistivity-switching active material are chalcogenides, carbon polymers, selected binary metal oxides such as nickel-oxide, tungsten-oxide, cupper-oxide, ternary metal oxides such as nickel-cobalt-oxide or even more complex metal oxides such as Cr-doped Sr(Ti)ZrO3 or Pr0.7Ca0.3Mn0.3.
An important criterion to select non-volatile memory technologies for high density levels will be the low-voltage operation of the memory cell. As supply voltages are scaled down, the operation voltages of the memory cell need also to be downscaled. Allowing lower supply voltages for the memory cell will result amongst other things in reduced power consumption, increased battery life, and reduced heating of the integrated circuit. As will be discussed below, the electro-forming process of an OxRRAM memory technology is of particular concern because it requires the application of several volts, typically 4-6V, during long times, typically more than the millisecond range. Regarding the thermal-induced reset mechanism, data retention of the ON state may be poor. Especially when using of nickel-oxide OxRRAM memories in the automotive segment where the memory cell has to function in a high temperature environment, the dependency of the reset mechanism on temperature may shown a weakness of the state-of-the-art nickel oxide OxRRAM memory cell. Hence it would be advantageous to eliminate the need for a “forming process”, to reduce the amplitude of the set and reset signals.